This invention relates to the production of laminated articles having magnetically encodable stripes printed thereon.
Cards having magnetically encoded stripes or other portions thereon are useful in many different applications. Such cards may be magnetically encoded identification cards, cards to program a calculator, or credit cards. While the present invention is useful in these and other areas, it is discussed in the context of a credit card, since there is great commercial interest in this area. It should be noted that the following discussion is applicable to other forms of magnetically encoded articles as well as credit cards. One common form of credit card is formed by utilizing a core stock of a material such as polyvinyl chloride acetate (PVCA) having opaque agents and plasticizers mixed in the polymeric matrix. The core stock is the layer of the card on which words, symbols and even pictures may be printed. In order to protect the core stock and give the card its shiny finish, surface laminates are used. A surface laminate may, for example, consist of a layer of polyvinyl chloride (PVC) or PVCA. A common, reliable way of providing a magnetically encodable stripe or panel is the transfer of magnetic medium to the laminate from a carrier under the influence of heat and pressure, commonly referred to as "hot stamping."
However, in the past several years, methods have been explored for printing magnetic stripes on cards. A preferred method of printing magnetic stripes is silk screening. Printing offers increased production rates with respect to provision of magnetic stripes using lengths of magnetic tape. Further, the shape of a magnetically encodable area which is printed is not restricted to the shape of a piece of tape. By printing magnetic areas having the shape of a circle, oval or an irregular shape may be provided if desired. Potential problems arise due to the nature of printing magnetic stripes on a lamina. Magnetic ink consists of magnetic oxide particles in a slurry which includes solvents. When the stripe is printed on the card, surface distortion of the stripe due to the action of the solvents on the lamina commonly results.
Non-uniformities in magnetic oxide distribution and in stripe surface flatness adversely affect the card's capability of providing useful readback signals when the card is placed in a card reader. In the reading process, a magnetic stripe is placed under a read head (or recording heads) which are quite sensitive to separation from the stripe. In the use of nominal read and recording heads, a magnetic layer cannot be more than 1/4 mil below the upper surface of a card. Further, non-uniformities in vertical distance, vertical being the direction normal to the plane in which the core stock lies, greatly affect signal to noise ratio in the electronic reading of characters from the card. The requirements for credit cards which are useful in standardized card readers are set forth in standard ANSI X4. 16-1973, American National Standard Magnetic Stripe Encoding for Credit Cards, published by the American National Standards Institute, New York, N.Y., 1976. This standard requires that the average peak-to-peak surface irregularity of the reading surface shall not exceed 15 microinches. It is further required that the surface stripe profile deviations from a straight line edge-to-edge shall be no more than 150 microinches for each 1/10 inch width of stripe.